The present invention relates to a film formation mask, an organic EL (Electroluminescent) panel formed by the film formation mask, and a method of manufacturing the organic EL panel.
The present application claims priority from Japanese Application No. 2003-74888, the disclosure of which is incorporated herein by reference.
An organic EL panel is produced by forming surface light emitting elements (based on luminescent areas of organic EL devices) on a substrate, and forming a display area by arranging one or more surface light emitting elements. The luminescent areas are formed by providing lower electrodes of various structures on the substrate, and then forming thereon a film pattern of an organic layer containing an organic luminescent layer, followed by forming thereon upper electrodes. Here, the film pattern is formed by using a film formation mask having openings corresponding to the film pattern, and accomplished by vapor deposition using the mask.
A process of forming an organic layer film pattern using the film formation mask can be described as follows. Namely, luminescent areas of organic EL devices are usually partitioned by an insulating film formed on the substrate. Then, the film formation mask having openings of slightly larger width than luminescent areas is used to form an organic layer film pattern on the luminescent areas. In particular, when a plurality of colors are to be displayed, it is required to use a film formation mask having openings corresponding to a desired pattern of different luminescent colors. Thus, by changing or sliding the mask at an appropriate timing, it is possible to paint different colors on the organic luminescent layer (Japanese Unexamined Patent Application Publication No. 2002-367787).
Here, the organic layer includes an organic luminescent layer and other layers (an electroluminescent layer, a hole transporting layer, an electron transporting layer, a hole injection layer, and an electron injection layer). Although an organic layer is usually in a multi-layer structure, it is also allowed to contain only single one layer which is an organic luminescent layer. Generally, even with a hole transporting layer and an electron transporting layer or the like (each formed of a single one kind of material and mounted on an identical substrate), it is allowed to use a film formation mask having different patterns corresponding to different luminescent colors in order to control film thickness in each area of each luminescent color (Japanese Unexamined Patent Application Publication No. 2001-237068).
To display a plurality of colors, there has been known not only the aforementioned method of painting different luminescent colors, but also CF Method and CCM Method in which an organic layer of a single color such as white or blue is formed and a color conversion layer based on a color filter or a fluorescent material is incorporated. Further, there is Photobleaching Method in which an electromagnetic wave is applied to a specific area on an organic layer of a single color so as to realize a multi-color emission. At this time, although it is not necessary to paint different colors to cover each color, it is required to use a film formation mask having a desired pattern in order to form an organic layer of a specific pattern in a display area.
However, even when only single one color is displayed, it was still required to use a film formation mask which has a predetermined pattern (usually, stripe-shaped pattern) corresponding to luminescent areas. At this time, in order to avoid a mask strength deterioration due to a dense distribution of openings, an opening pitch (an interval between every two adjacent openings) is enlarged, thereby forming an organic layer film pattern in the display area of a display panel by dividing a film formation process into several steps (Japanese Unexamined Patent Application Publication No. 2000-48954).
In using a film formation mask for forming luminescent areas of organic EL devices on a substrate (i.e., when the mask is placed on the substrate), a tension is usually added to the perimeter of the mask to avoid the slacking of the mask, thereby keeping the entire mask in a completely flat state. However, with the addition of the tension to the perimeter of the mask, distortion will occur in the outermost openings of the film formation mask irrespective of the shape of these openings. Then, once film pattern is formed on the substrate through the deformed openings, film pattern disorder will occur near the outmost edges of the display area, resulting in deteriorated display performance near the outermost edges of the display area. Consequently, it becomes impossible to ensure an appropriate display in the entire display area.
Moreover, it is known that an organic layer of each organic EL device will be deteriorated due to an unavoidable contact with the surrounding atmospheric air, since moisture and oxygen existing in the surrounding atmospheric air can cause such deterioration. In order to prevent such deterioration, an entire display area of an organic EL panel is usually covered by an encapsulation member. In detail, an adhesive agent is applied to the substrate outside the display area so as to form an adhesive-applied perimeter around the display area. Then, an annular area along the perimeter of the encapsulation member is tightly bonded to the adhesive-applied area of the substrate, thereby protecting the entire display area of organic EL panel from the surrounding atmospheric air.
However, since an adhesive agent for use in the capsulation also contains moisture, oxygen or the like which can deteriorate the organic layer, when such an adhesive agent get into contact with the organic layer, the moisture and oxygen or the like will invade into the organic layer and thus cause the organic layer to be deteriorated. In particular, if an amount of the adhesive agent applied is too large, the applied adhesive agent will spread towards the display area once the encapsulation member is pressed onto the substrate, hence causing the adhesive agent to contact the outer edge of the display area. As a result, the display performance will be deteriorated near the outermost edge of the display area, making it impossible to ensure an appropriate display in the entire display area.